The present invention relates to a method for producing a frozen xe2x80x9cyubaxe2x80x9d.
A xe2x80x9cyubaxe2x80x9d is made from soybean milk like tofu. When soybean milk as a starting material is heated to a temperature at which boiling is still avoided, its surface forms a film, which is lifted up with a skewer or wire as a fresh xe2x80x9cyubaxe2x80x9d. Among such films, the very first film lifted up with soybean milk is called as a fresh lifted-up xe2x80x9cyubaxe2x80x9d, whose flavor and texture are excellent especially. A dried xe2x80x9cyubaxe2x80x9d is made by means of spontaneous drying or hot air drying of a fresh xe2x80x9cyubaxe2x80x9d.
A fresh xe2x80x9cyubaxe2x80x9d or fresh lifted-up xe2x80x9cyubaxe2x80x9d is recently not only consumed in a first-class Japanese restaurant but also purchased from a tofu shop or first-class Japanese restaurant through mail-order selling or over-the-counter selling. However, it is distributed only by chilled-marketing since it is denatured and becomes harder when being frozen, resulting in a substantial restriction in distribution and marketing. Thus, since a fresh xe2x80x9cyubaxe2x80x9d or fresh lifted-up xe2x80x9cyubaxe2x80x9d which preserves a smooth mouthfeel and a soybean milk flavor has not been pasteurized, its shelf life is as short as one or two days after being marketed. On the other hand, a dried xe2x80x9cyubaxe2x80x9d has a low water content, which gives it a longer shelf life, but it has a hard mouthfeel and a less preferable flavor.
When only a xe2x80x9cyubaxe2x80x9d is sterilized by heating in order to improve storability, the xe2x80x9cyubaxe2x80x9d becomes coagulated and its mouthfeel becomes hard. On the other hand, when it is frozen for improving storage stability, it undergoes frozen denaturation, resulting in a hard and stiff mouthfeel once being thawed. Thus, its way of marketing is restricted because it can not be subjected to frozen storage.
In order to prevent any freezing denaturation, JP 2001-57860 A discloses the addition of 0.1 to 25% of saccharides to soybean milk used for producing a fresh xe2x80x9cyubaxe2x80x9d whereby preventing the freezing denaturation, or the addition of 0.1 to 25% of saccharides to soybean milk in which a xe2x80x9cyubaxe2x80x9d is soaked. However, the invention of this patent application fails to obtain the desired smooth mouthfeel and flavor which are experienced with a fresh lifted-up xe2x80x9cyubaxe2x80x9d. Further, there is no difference in storability after thawing between the product of this patent application and a commercially available fresh xe2x80x9cyubaxe2x80x9d by chilled distribution because the product is not subjected to heating before freezing.
JP 3-201960 A discloses improvement of chilled storage stability by filling soybean milk together with a xe2x80x9cyubaxe2x80x9d in a casing and then heating. However, this patent application is silent on frozen distribution since it has been a matter of a common knowledge of those skilled in the art that a xe2x80x9cyubaxe2x80x9d can not be frozen. Further, a fresh xe2x80x9cyubaxe2x80x9d which has not been subjected to any drying process undergoes, when being heated together with soybean milk, a re-dissolution in the soybean milk, resulting in the loss of the original form of the xe2x80x9cyubaxe2x80x9d.
Thus, a method for producing a frozen xe2x80x9cyubaxe2x80x9d capable of exhibiting a smooth and satisfactorily flavored mouthfeel like that of a fresh lifted-up xe2x80x9cyubaxe2x80x9d, which has a long shelf life after being thawed, has not yet been invented.
Accordingly, the present invention provides a xe2x80x9cyubaxe2x80x9d which exhibits a mouthfeel and a flavor comparable with those of a fresh lifted-up xe2x80x9cyubaxe2x80x9d, even after being frozen and then being thawed.
The present invention is a method for producing a frozen xe2x80x9cyubaxe2x80x9d comprising heating and freezing a xe2x80x9cyubaxe2x80x9d whose water content has been adjusted at 60% or less together with soybean milk. The heating together with soybean milk is preferably carried out under conditions of 70 to 100xc2x0 C. at which sterilization effect is expected. Further, the concentration of the soybean milk is adjusted to 2 to 12 Bx, preferably 4 to 10 Bx and a mixing ratio of the xe2x80x9cyubaxe2x80x9d, and the soybean milk is adjusted to 1:1 or higher, preferably 1:10.
In the present invention, a xe2x80x9cyubaxe2x80x9d should be employed after being subjected to a drying step so that its water content becomes 60% or less, preferably 30 to 50%, and this step serves to strengthen the protein binding in the xe2x80x9cyubaxe2x80x9d and to allow the resistance to be exerted in the subsequent heating step in the presence of soybean milk. Thus, when a xe2x80x9cyubaxe2x80x9d whose water content is 60% or higher, i.e., a so-called fresh xe2x80x9cyubaxe2x80x9d is subjected to the subsequent heating step, an almost complete dissolution in the soybean milk with its original form being lost, resulting in a remarkable reduction of commercial value.
When a xe2x80x9cyubaxe2x80x9d is heated in the absence of soybean milk, the xe2x80x9cyubaxe2x80x9d becomes hard, and, in case that several films are stacked, films adhere to each other, which makes it difficult to separate into single individual films. In order to obtain a separated single individual film, it is essential to use soybean milk which serves as a lubricant.
For reducing the water content to 60% or less, a xe2x80x9cyubaxe2x80x9d may be dried for example by spontaneous drying or hot air drying. A xe2x80x9cyubaxe2x80x9d whose water content has been once adjusted may be stored frozen and then may be used as it is or after thawing.
When a xe2x80x9cyubaxe2x80x9d is subjected to a freezing step, its mouthfeel and flavor is deteriorated. By taking into this, the present inventors have studied heating of xe2x80x9cyubaxe2x80x9d together with soybean milk so as to adjust its mouthfeel before freezing to a soft and smooth mouthfeel with providing the flavor and taste of the soybean milk with the xe2x80x9cyubaxe2x80x9d to obtain a xe2x80x9cyubaxe2x80x9d having tenderness, smoothness and a flavor similar to those of a fresh lifted-up xe2x80x9cyubaxe2x80x9d.
A xe2x80x9cyubaxe2x80x9d having a water content of 60% or less can be freely imparted with the desired tenderness which may vary from that of a fresh xe2x80x9cyubaxe2x80x9d to that of a fresh lifted-up xe2x80x9cyubaxe2x80x9d by adjusting the heating conditions. Moreover, even a dried xe2x80x9cyubaxe2x80x9d having a pool flavor can be imparted with a good soybean taste by increasing the concentration of the soybean milk used here.
In order to further improve taste, soybean milk used may be supplemented with auxiliary materials capable of improving soybean flavor, saccharides, sweeteners and starch degradation products for modifying the sweetness of a soybean paste, liquid tofu, soybean flake or soybean milk, as well as seasonings including Japanese taste seasonings, western taste seasonings, Chinese soup seasonings, miso, sesame (ground sesame or sesame paste), soy sauce, salt, and the like to obtain a completely different flavor.
Besides, a concentration of soybean milk of 12 Bx or higher is not preferred since it causes remarkable frozen denaturation of the soybean milk.
A poorly film-formed xe2x80x9cyubaxe2x80x9d (one whose water content exceeds 60% such as fresh xe2x80x9cyubaxe2x80x9d, fresh lifted-up xe2x80x9cyubaxe2x80x9d, pick-up xe2x80x9cyubaxe2x80x9d) is not preferred since it dissolves in soybean milk almost entirely upon heating.
The heating conducted herein serves not only as a means for heating a hard and poorly flavored dried xe2x80x9cyubaxe2x80x9d together with soybean milk to produce a soft and highly flavored xe2x80x9cyubaxe2x80x9d but also as a heat sterilization means. Because of this heating step, the xe2x80x9cyubaxe2x80x9d becomes a heated product before freezing and therefore, it can be stored for a period as long as two weeks in a refrigerator after being thawed. Thus, the xe2x80x9cyubaxe2x80x9d can be consumed safely even in the summer in addition to the three other seasons.
The terms used in the present invention will be illustrated.
First, a xe2x80x9cyubaxe2x80x9d means a film formed on the surface of heated soybean milk and lifted up by a skewer or wire. A xe2x80x9cyubaxe2x80x9d which has not been dried is referred to as a fresh xe2x80x9cyubaxe2x80x9d, among which the very first film lifted up with soybean milk is referred to as a fresh lifted-up xe2x80x9cyubaxe2x80x9d, whose flavor and texture are excellent especially and whose water content exceeds 60%. A xe2x80x9cyubaxe2x80x9d which was subjected to spontaneous drying or hot air drying is referred to as a dried xe2x80x9cyubaxe2x80x9d.
The soybean milk used herein may be any soybean milk, including those obtained by hot grinding or cold grinding. The soybean milk having a concentration of 2 to 12 Bx, preferably 4 to 10 Bx, is used and the ratio between a xe2x80x9cyubaxe2x80x9d and soybean milk used together is generally 1:1 or higher, preferably 1:10, though it may vary depending on the degree of dryness of the xe2x80x9cyubaxe2x80x9d as well as the soybean milk concentration. When a concentration of soybean milk is too low, or mere water is used, mouthfeel of after thawing becomes harder. Further, when an amount of soybean milk relative to a xe2x80x9cyubaxe2x80x9d is too small, or soybean milk is not added, mouthfeel of after thawing mouthfeel becomes harder and, if several xe2x80x9cyubaxe2x80x9d films are stacked, separated single individual films cannot be obtained because they firmly adhere to each other.
When a xe2x80x9cyubaxe2x80x9d and soybean milk are used in a ratio of 1:1 or higher, there is no problem and, when they are combined with a Chinese soup seasoning, a soybean milk soup containing xe2x80x9cyubaxe2x80x9d can be served. Further, when a soup or a Chinese soup mix together with a Chinese noodle are added thereto, a soybean milk noodle containing xe2x80x9cyubaxe2x80x9d can be served. Furthermore, when a cooked rice is added thereto, a xe2x80x9cyubaxe2x80x9d rice porridge can be served.
When a xe2x80x9cyubaxe2x80x9d and soybean milk are contained in a retort pouch, the heating may be carried out with or without sealing the pouch. The heating may also be carried out by using a cooking pot or by steam heating in a stainless-steel vat. The heating is carried out at 70 to 100xc2x0 C., preferably 80 to 90xc2x0 C., for a period of 5 to 120 minutes, preferably 30 to 60 minutes, followed by freezing. The freezing is preferably a quick-freezing.
While the thawing of the resultant product for eating may be spontaneous thawing or heating thawing, it is preferably carried out using a microwave or by boiling.